The goal of this research is to understand chromatin mechanisms that maintain gene expression states during development. Polycomb group (PcG) proteins control cell fate decisions in development by creating specific chromatin modifications that lead to transcriptional silencing. Discovered in Drosophila, they are essential regulators of Hox gene expression along the anterior-posterior axis, providing molecular memory of special cues in the early embryo. PcG proteins are highly conserved from flies to humans, where they have been demonstrated to play key roles in the maintenance of stem cell pluripotency and cancer pathologies. This research will investigate key molecular roles of PcG complexes and their interacting proteins. Specifically, this work will focus on Polycomb repressive complex 2 (PRC2), a histone methyltransferase (HMTase) complex that methylates histone H3 on lysine 27. The first Aim will assess the relationship of PRC2 with the fly Jarid (Jumonji plus ARID domain) proteins. Although the mammalian Jarid proteins have recently been shown physically interact with and influence the HMTase activity of mammalian PRC2, the relationship between the fly Jarids and PRC2 has not been tested. The second Aim addresses in vivo consequences of H3K27me3 in the absence of PRC2. Using a heterologous HMTase, the role and sufficiency of H3K27me3 to elicit transcriptional silencing will be assessed. Artificially targeting this heterologous HMTase to distinct regions upstream, within or downstream of a gene will determine the positional requirements of chromatin modifications for target silencing. These Aims will be accomplished using molecular, biochemical and genetic methods including chromatin immunoprecipitation, enzyme assays, protein purification, chromosome immunostaining and loss-of-function analysis. These Aims will advance knowledge of the regulation and function of PRC2 in its role in chromatin silencing in development.